I just ran a dnf update on my fedora 26 box and the build and install of the nvidia akmod failed:
2017/08/28 07:28:04 akmods: Installing newly built rpms 2017/08/28 07:28:04 akmods: DNF detected error: db5 error(-30969) from dbenv->open: BDB0091 DB_VERSION_MISMATCH: Database environment version mismatch error: cannot open Packages index using db5 - (-30969) error: cannot open Packages database in /var/lib/rpm Error: Error: rpmdb open failed 2017/08/28 07:28:04 akmods: Could not install newly built RPMs. You can find them and the logfile 2017/08/28 07:28:04 akmods: 375.66-3-for-4.12.8-300.fc26.x86_64.failed.log in /var/cache/akmods/nvidia/
After getting the system back up, I manually installed the rpm it built via dnf install and it seemed to install fine.
What the heck happened during the initial dnf update?